FIG. 18 illustrates a configuration of an AD converter 900 that can perform analog-digital conversion (AD conversion) on measurement target voltages for a plurality of channels. In the AD converter 900, the measurement target voltages for the plurality of channels are input to an analog processing part 910. The analog processing part 910 generates a plurality of analog voltage signals corresponding to the measurement target voltages for the plurality of channels (analog voltage signals for the plurality of channels) through a process of generating a divided voltage of each of the measurement target voltages or amplifying each of the measurement target voltages. A signal selection part 920 includes a multiplexer, and selects one of the plurality of analog voltage signals from the analog processing part 910 to output the selected analog voltage signal to an AD conversion part 930. At this time, amplification (impedance conversion) of the selected analog voltage signal or high frequency reduction processing is appropriately executed. The AD conversion part 930 performs AD conversion on the analog voltage signal provided from the signal selection part 920 to obtain a digital signal. By sequentially switching channels selected by the multiplexer, it is possible to sequentially perform AD conversion on the measurement target voltages for the plurality of channels in a time division manner.
In the AD converter 900 of FIG. 18, various abnormalities (failures) may occur. For example, an abnormality in which the multiplexer in the signal selection part 920 cannot normally perform a selection operation, an abnormality in which a wiring for propagating an output signal of the analog processing part 910 is grounded or short-circuited, or an abnormality in which a wiring for propagating an output signal of the signal selection part 920 is grounded or short-circuited may occur. In addition, an abnormality in which a gain error or an offset error of the AD conversion part 930 becomes excessive beyond a design range may occurs.
However, the AD converter 900 of FIG. 18 cannot recognize the occurrence of such an abnormality even if the abnormality has occurred. If an abnormality can be recognized when it occurs, there is a great merit that a protection operation corresponding to the abnormality (for example, an operation stop or failure notification based on an erroneous AD conversion result) can be performed.
Furthermore, although the AD converter that performs AD conversion on the measurement target voltages for the plurality of channels has been described, similar situation exists for an AD converter that performs AD conversion on one measurement target voltage (however, the latter AD converter does not have any abnormality regarding the signal selection part 920).